Substrate wetting agents are interface-active compounds which lower the surface tension especially of aqueous varnish and paint formulations in order thus to promote for example the substrate wetting and also the flow. Substrate wetting agents are especially important for avoiding defects in the coating film when the substrate has a low surface tension (such as polymeric films, for example) or is contaminated with oily substances.
Substrate wetting agents are available in liquid and solid forms and often the commercially available products constitute mixtures of different interface-active compounds. It is considered common general knowledge here that such interface-active compounds have amphiphilic character—that is, they are generally composed of molecules with a hydrophilic and a hydrophobic moiety. Typical hydrophilic building blocks of these amphiphiles are anionic groups or ethylene oxide units. Nowadays use is often made of what are called alkylphenol ethoxylates—which increasingly, however, are preferably avoided on environmental protection grounds. Established alternatives to the alkylphenol ethoxylates include the alcohol ethoxylates, i.e., adducts of ethylene oxide with (hydrophobic) alcohols. A disadvantage of the alkylphenol ethoxylates and also of many alcohol ethoxylates is the frequently foam-stabilizing effect of these substrate wetting agents. The foam which forms during the production and processing of paints and varnishes disrupts the processing operations and interferes with handling, and is therefore suppressed—at cost and inconvenience—using foam-destroying additives.
In order to counter the problem of foam stabilization, a variety of products have been developed in the past. Alcohol alkoxylates are often used, for example, as low-foam wetting agents. Typical commercially available alcohol alkoxylates consist in general of linear or branched alcohols which have been reacted with ethylene oxide (EO) and optionally, additionally, with propylene oxide (PO) or else with higher epoxides (e.g., butylene oxide, BuO). As the skilled person is aware, the purpose of EO units is to construct the hydrophilic moiety of the molecule, while the alkyl radicals (originating from the alcohol building block) and also the PO units form the hydrophobic moiety of the molecule.
Also known (see WO-A-2009/061452 and EP-A-681,865) is the formulation of alcohol propoxylates in combination with other surfactants and the use of such formulations as low-foam cleaners.